Abstract: Aluminum hydroxide having a particle size of 2 to 30 .mu.m and having small specific surface area and low resin filling viscosity can be prepared by using precipitated aluminum hydroxide composed of secondary agglomerated particles having a primary particle size almost equal to the desired average particle size of intended pulverized aluminum hydroxide as the starting material to be pulverized and pulverizing this starting aluminum hydroxide. This aluminum hydroxide has an average particle size of 2 to 30 .mu.m, a surface roughness coefficient Sr/Sc (in which Sr represents the specific surface area of particles measured by the nitrogen adsorption method and Sc represents the specific surface area calculated from the size of particles approximated to spheres while taking the particle size distribution of particles into consideration) smaller than 2.5 and a linseed oil absorption smaller than 30 cc/100 g as determined according to JIS K-5101.

Abstract: Bayer liquor containing carbon compounds is freed from the carbon compounds by a method which comprises adjusting the molar ratio of the aluminum component to the sodium component in the liquid to a value in the range of from 1 to 5 calculated as Al.sub.2 O.sub.3 /Na.sub.2 O and heating the resultant Bayer liquor.